Previously, various types of head-up display devices have been proposed. In these head-up display devices, a display light, which is outputted from a display unit, is reflected by a reflecting mirror and is projected to a front glass, so that a driver of the vehicle visually recognizes a display image that is superimposed on a scene at a front side of the vehicle. In the head-up display devices described above, particularly under a high temperature environment, there are disadvantages, such as damaging of the display unit caused by heating, a requirement of a long time period (e.g., one hour or longer) until a brightness of the display unit is sufficiently increased since the time of starting the operation. In order to address the above disadvantages, there has been proposed a head-up display device that includes a cooling fan as a cooling means for cooling the display unit that generates the display light. One such a device is disclosed in the patent literature 1.